An electro-chemical finishing method which has been referred to as a metal finishing method is disclosed in, for example, Japanese Patent Laid-Open Publication No. 255013/1987. This electro-chemical machining method involves supporting an electrode and workpiece opposite to each other with a predetermined gap therebetween, and finishing the workpiece by repeating in an alternating manner the supply of a direct current between the electrode and workpiece and the injection of electrolyte into the gap.
With the above-described electro-chemical finishing method, however, disadvantages are encountered because, in this method, after the supply of direct current, electrolytic products generated between the poles are expelled by raising the electrode from the position in which the direct current was supplied and by injecting electrolyte through holes formed in the electrode.
Namely, if electric-discharge die sinking is performed using the electrode or workpiece having a through hole for injecting electrolyte, although the workpiece is in general processed or finished over a large area, electrolytic products produced from the workpiece and present in the gap cannot be expelled simply by raising the electrode and injecting electrolyte after supplying direct current, thereby making it difficult to replace the contaminated electrolyte in the gap with fresh electrolyte. As a result, part of the contaminated electrolyte remains in the gap, causing a variation in the finishing conditions for various portions of the surface of the workpiece to be finished. As a result, the required finishing is hindered, the dimensions are varied and the improvement of the surface roughness is delayed. As a result, it is impossible to obtain within a short time a glossy surface having a highly precise surface quality.
Therefore, an object of the present invention is to provide a finishing method employing an electrochemical process which is capable of limiting variation in dimension regardless of the size and configuration of the surface of the workpiece to be finished, and which is capable of improving the surface roughness of the workpiece surface, the method being thus capable of stably providing a glossy surface having a highly precise surface quality within a short time.